The Butterfly Society of Virginia
Jeanne Hart Petterson's 1997 Article on Growing Milkweeds
This article first appeared in the Summer 1997 issue of the Butterfly Bulletin. The version below is from a later version which appeared in the Winter 2002 Butterfly Bulletin. Most recently an excerpt from this article appeared on page 5 of the Winter 2008 Butterfly Bulletin.
Growing and Propagating Milkweeds
By Jeanne Hart Petterson
If you like Monarchs (and who doesn’t), then you need to grow milkweeds. Monarch adults and larvae have bold orange, yellow, white, and black patterns, coloration which warns potential predators that they contain poisonous chemicals. Monarchs get their poisonous chemicals from the milkweed plants they eat as larvae.
Varieties of Asclepias:
Dr. Richard Mills’ outstanding article on “Milkweed and Monarchs” was reprinted in the Fall 2001 issue of the Virginia Butterfly Bulletin. He identified 13 species of Asclepias (milkweeds) that grow in Virginia, and classified their suitability as Monarch host plants.
Unfortunately, few varieties of milkweed are available in local garden centers; these include Asclepias tuberosa (butterfly weed) and Asclepias incarnata (swamp milkweed), both of which were cited by Dr. Mills as suitable Monarch host plants. I’ve grown only a small subset of the 108 known North American species of Asclepias and milkweeds (Dr. Mills stated that 27 of these are known to be host plants for Monarchs). I’ve grown butterfly weed, swamp milkweed, Asclepias currassavica (bloodflower), Asclepias syriaca (common milkweed), and Asclepias verticillata (whorled milkweed). Of these, I’ve found that butterfly weed is the least favorite of my Monarch guests in my Virginia Beach garden for laying eggs (perhaps the leaves are tougher?) The bloodflower seems to be the #1 favorite with it’s tender tropical leaves, with swamp milkweed and common milkweed running close seconds. I also grow Oxypetalum caeruleum, with it’s lovely star-shaped light blue flowers and milkweed pods, which is reported to be a food source for Manarch larvae; however, I haven’t yet observed a Monoarch egg or larvae on this plant. If you have seeds or plants for other species of Asclepias, please contact me for a trade!
Landscaping with Milkweeds:
Asclepias can be easily integrated into your garden. Swamp milkweed is available in pink shades and white. Butterfly weed flowers are normally orange, but are also available in yellow and red shades. Bloodflower flowers are an orange/yellow mix. I like to combine bloodflowers and butterfly weed in beds with cosmos, zinnia, day lilies, coreopsis, gold buddleia, lantana, and black-eyed Susans. Swamp milkweed works well with purple lantana, pink or blue shades of buddleia, pink shades of annuals (gomphrena, zinnia, cosmos), and purple coneflower. I personally like to combine colors to produce more of a natural look.
Asclepias tuberosa is the shortest of the group (12 to 18” height). Swamp milkweed and bloodflower grow to 24” to 30” tall. A full sun or part shade location is best. In your garden, choose a well drained, sunny location for your butterfly weed and common milkweed. Choose a more rich, moist location for swamp milkweed.
I’ve found that the number of Monarchs I have in my garden expands exponentially with the number of Asclepias plants. Monarchs may not notice a single butterfly weed or milkweed plant, but they do notice a group of them. They even notice the Asclepias plants when they’re tiny, just emerging from winter dormancy in April. This year, my 2” Asclepias – all varieties – were covered with Monarch eggs. The migrating female Monarchs seem frantic to find the Asclepias, brushing against different plants until they found an Asclepias to lay an egg on. Because Monarch caterpillars are such voracious eaters, female Monarchs typically lay a single egg on the underside of a leaf. There, if you see multiple eggs on a single plant, they may be from multiple females.
I was amazed this year to watch a single older migrating female Monarch lay her eggs on the flats of Asclepias seedlings on my deck for at least four hours. How many eggs did she lay? I’m not sure, but nearly every seedling had at least one egg (over 100) by the time she was done!
Propagation of Asclepias:
Propagation of milkweeds is difficult, but achievable, once you know the tricks! Division of milkweeds is not recommended. In fact, the one cardinal rule in caring for milkweeds is that, once planted, the plants should not be moved. Tap roots are long, and, once damaged, often don’t recover. (Note – this is not the case with bloodflower, which can be easily transplanted at any stage of growth.)
Growing and Propagating Milkweeds
Starting milkweeds from seed is the most common method of propagation; however, most varieties of milkweed require a cold treatment before sowing! Stratification exposes dormant seeds to a period of chilling. Mix a single species of milkweed seeds with one to three times their volume of a moist (but not wet) medium such as sand, peat moss, sphagnum moss, or vermiculite. Place mix and seeds in a box, can, glass jar with perforated lid, plastic bag, or other container that provides aeration. Stratification of milkweeds usually occurs best at 32 to 41˚F for a period of three to six weeks. After stratification, remove the container from the refrigerator or freezer and thaw. You can separate the seeds from the medium, or alternatively, allow the seeds to remain in the stratification medium for the germination process. Sow seeds immediately. Best germination is at 65 to 80˚F. Use bottom heat and fluorescent lights, if available, for best results. Bloodflower and other tropical species of milkweeds do not require stratification.
I have also successfully propagated bloodflower, butterfly weed, and swamp milkweed from cuttings. Other milkweed species can also be propagated in this manner. Propagation by stem cutting is the preferred method for propagating any plant, including milkweeds, with a specific form, flower color, or other characteristic that you wish to duplicate exactly (such as a yellow or red flower color on butterfly weed). Cut a milkweed stem on an angle at least Ľ” below a leaf node. The cutting should be about three to six inches long. You may wish to cut the stems underwater, however, I have had success with stem propagation without the “cutting underwater trick”. Remove any leaves from the lower two to three inches, leaving at least one or two sets of leaves on top. Dip the cutting in hormone powder, such as Rootone, make a hole in moisteded soilless mix or other propagation media, and insert the cutting. Firm soil around cutting, label, and cover with a plastic bag or glass to increase humidity if the air is dry. Watch for signs of moisture buildup in the bag, and keep cuttings well ventilated to prevent disease. After a few days, remove the plastic. Keep new cuttings out of direct sun for a few days, then place in a protected area out of hot sun and winds, such as under deck benches or under tall trees.
Care of Milkweeds:
Milkweeds are easy to care for. I lightly clip or pinch Asclepias tuberosa when small to produce bushier plants (make sure there aren’t any eggs or larvae on the plant before clipping).
Collect and remove Asclepias seed pods after they’re ripe (don’t wait too long, or they will blow away). Remove and dry the brown seeds and save them for later propagation. With early seed pod removal, some Asclepias will rebloom. I have often seen butterfly weed bloom for several months! Allow the collected seeds to dry for a week or two, then store your milkweed seed pods in the garage, a refrigerator, or a cool dry place indoors. Common milkweed and bloodflower will often self-seed in Hampton Roads and other areas in Virginia, depending upon winter weather.
Asclepias are prone to several insect pests. These include the orange milkweed aphid and other small black bugs. The aphids are difficult to get rid of. I will not use chemical insecticides, as they may kill my Monarch eggs and larvae. I have tried Safer Soap and hard sprays of hose water with disappointing results. Generally, these aphids will not disturb the milkweeds or the Monarch larvae – in other words – ignore them and they will eventually go away.